[gnome-boxes] display: Add file transfer API

[Felipe Borges <felipeborges src gnome org>]

commit 2018ecb553236900ce29426852048c7e779576e7
Author: Visarion Alexandru <viorel visarion gmail com>
Date:   Wed Oct 25 17:16:59 2017 +0300

    display: Add file transfer API
    
    Add virtual method transfer_files() and virtual property
    can_transfer_files, which currently defaults to false for
    all display types.
    
    This will help us create a more explicit file transfer
    between host and SPICE guest machines in following patches.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=762321

 src/display.vala | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/display.vala b/src/display.vala
index c42a06b5..73b4e737 100644
--- a/src/display.vala
+++ b/src/display.vala
@@ -4,6 +4,7 @@
 private abstract class Boxes.Display: GLib.Object, Boxes.IPropertiesProvider {
     public abstract string protocol { get; }
     public abstract string? uri { owned get; }
+    public virtual bool can_transfer_files { get { return false; } }
 
     public BoxConfig? config { get; protected set; }
     public bool can_grab_mouse { get; protected set; }
@@ -35,6 +36,8 @@ public virtual bool should_keep_alive () {
 
     public virtual void collect_logs (StringBuilder builder) {
     }
+    public virtual void transfer_files (GLib.List<string> uris) {
+    }
     public abstract void send_keys (uint[] keyvals);
 
     public abstract List<Boxes.Property> get_properties (Boxes.PropertiesPage page);